Cable locking and sealing process for sensor

ABSTRACT

A sensor has a metal case with a sensing coil at one end and a shielded cable extending from the other. In one use it is placed in proximity to rotating machinery to sense imbalance by position change of the shaft. A pair of suitably sized metal cylinders which are precisely interlocked by dielectric material provides for firm mechanical and electrical connections to the inner and outer conductors of the associated shielded cable. In addition a four step injection molding process provides for accurate and secure location of the sensing coil. And at the same time the entire structure because of the injection molding and associated seals is moisture proof. Other uses include temperature and velocity sensing. 
     In an alternative embodiment only a two-step injection molding process is utilized with a somewhat simplified procedure.

This is a continuation-in-part of application Ser. No. 07/887,177 filedMay 21, 1992, now abandoned.

The present invention is directed to an improved cable locking andsealing process for a sensor and more specifically to a moisture proofsensor and a process for making such sensor which is used to sensevibration of rotating machinery, temperature sensing and other purposes.

BACKGROUND OF THE INVENTION

For sensing the vibration of motor shafts, for example, of largerotating machinery, a proximity sensor is utilized. Such a sensor has ametal case which contains a sensing coil at one end and has a shieldedcable extending out from the other end of the case for connecting to anelectrical processing unit. By well known techniques, excessive movementof the shaft indicating unwanted vibration can be sensed. This providesan indication of incipient problems. Such a system with a proximitysensor is at the present time being sold by the assignee of thisapplication, Bently Nevada Corporation of Minden, Nev.

Because of the very adverse ambient conditions such sensor operatesunder, it must be resistant to heat and moisture and also withstandmechanical stresses such as pulling or twisting on the shielded cable.One sensor which is sold at the present time by the assignee of thisapplication is shown and described in the process patent U.S. Pat. No.5,016,343 and apparatus patent U.S. Pat. No. 5,021,737.

OBJECTS AND SUMMARY OF THE INVENTION

It is a general object of the present invention to provide an improvedsensor and a method of making such sensor.

In accordance with the above object there is provided a process formaking a sensor with a sensing coil at one end having at least one leadand a shielded cable extending out of the other end for connecting to anelectrical processing unit, the cable having an outer insulating jacketand an outer shielding conductor surrounding an inner insulator carryingat least one interior conductor. The process comprises the steps oftrimming an end of the cable so that the jacket and outer shieldingconductor is cut away to expose an end segment of the interiorconductor. At least one metal cylinder is formed having an inner cavityto accommodate said interior conductor. In one injection molding stepwith bondable dielectric material, a cylindrical jacket is molded overthe cylinder and also provides a coil recess near said cylinder andsubstantially coaxial therewith and also provides at least one tunnelleading from the recess and terminating at the cylinder. The coil isinserted in the coil recess while inserting the lead through the tunneland electrically attached to the cylinder. In another injection moldingstep at least the coil is encapsulated with the bondable dielectricmaterial.

In an alternate technique, in the first injection molding step anannular bobbin recess is also provided and after the recess is formed, acoil is formed in the shape of a bobbin and placed in the recess and itsleads welded respectively to the front and back cylinders. After thestep of inserting the trimmed cable and fixing it to the back and frontcylinders, a protective sleeve is placed over the coil and leads andthen in a final injection molding step a cylindrical jacket is moldedover the front and back cylinders bonding to the bridging materialincluding forming a cover on the face of the coil and bobbin recess.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is an elevational view of a proximity sensor incorporating thepresent invention which is partially cut away and somewhat simplified.

FIG. 2 is a simplified cross-sectional view of a portion of FIG. 1 andwhich illustrates a first molding step.

FIG. 3 is a simplified exploded view of a portion of FIG. 1.

FIG. 4 is an enlarged cross-sectional view taken along lines 4--4 ofFIG. 3.

FIG. 5 is a diagrammatic elevational view illustrating a second moldingstep of the present invention utilizing the structure illustrated inFIG. 3.

FIG. 6 is a diagrammatic view of an assembly step.

FIG. 7 is a cross-sectional view illustrating a third molding step ofthe present invention.

FIG. 8 is an exploded view illustrating a fourth molding step showinghow the sensor of FIG. 1 is produced.

FIG. 9 is a cross-sectional view of apparatus of the present inventionillustrating the steps of the invention.

FIG. 10 is a cross sectional view illustrating the combination ofportions of FIG. 9.

FIG. 11 is an exploded view illustrating another step of the invention.

FIG. 12 is an exploded view illustrating another step of the invention.

FIG. 13 is an elevational showing the completion of the steps of FIGS.11 and 12.

FIG. 14 is a cross-sectional view similar to FIG. 10 illustratinganother step of the invention.

FIG. 15 is a cross-sectional view illustrating another step of theinvention and the combination of the elements of FIGS. 13 and 14.

FIG. 16 is a cross-sectional view of showing the combination of units ofFIG. 15.

FIG. 17 illustrates another step of the invention.

FIG. 18 is a cross sectional view showing the combination of theexploded portions of FIG. 17.

FIG. 19 is an exploded cross-sectional view showing another step in theinvention.

FIG. 20 is a cross-sectional view illustrating the completed invention.

FIG. 21 is a cross-sectional view similar to FIG. 20 of anotherembodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 shows a cross sectional and simplified cutaway view of the sensorof the present invention. In this embodiment it is a proximity sensor;but the invention is applicable to other sensors such as temperature orvelocity as will be discussed below. It includes a metal threaded case10 having a front end sensing coil 11 (in the form of a bobbin) andtowards its back end a coaxial cable 12 which effectively extends fromthe case 10 for connection to an electronic processing unit which is notshown. In general the coil 11 is in proximity to a rotating shaft and achange of position of the shaft with respect to the coil changes theelectrical characteristics of coil 11. This is sensed by the associatedelectronic processing unit 2, for example, give an alarm signal ifeccentric movement of the shaft exceeds a predetermined amount.

The coaxial cable 12 which is also better shown in FIG. 3 is of standardconstruction (except for minor variation as will be discussed below) andincludes a center interior conductor 13, an outer shielding conductor 14(which in the present embodiment is braided but may be a solid dependingon desired flexibility), and an outer insulating jacket 16. Outerconductor 14 and center conductor 13 are separated from one another byan inner cylindrical insulator 17a and 17b. The insulator in this caseis in the form of two layers but is typically a single layer incommercially available coaxial cables.

FIG. 4 illustrates these two layers in the cross-sectional view andwhich is not to scale for purposes of clarity. In general the purpose ofthe use of the two layer inner cylindrical insulators 17a and 17b is toallow a smaller diameter inner insulating portion 17a so that when itinterfaces with the remaining structure, the final diameter of theproximity sensor can be relatively small or miniaturized.

Now referring again specifically to FIG. 1, in its completed form thecenter conductor 13 extends through the center cavity 21 of a frontmetal cylinder 22 and has a diameter substantially equal to the diameterof cavity 21. The outer diameter of the outer conductor 14 issubstantially equal to the diameter of an inner cavity 23 of a backmetal cylinder 24. This is better shown in FIG. 2 where the front andback metal cylinders 22 and 24 are shown by themselves but assembled orinterlocked in spaced coaxial proximity by the bridging dielectricmaterial 26. Although not shown in detail in the drawing of FIG. 2 (orfor that matter of FIG. 1), the dielectric material forms an interlockwith the smaller diameter end 27 of back cylinder 24 by the use of fourholes in the end of section 27 which the dielectric material fills.

The interlocked front and back cylinder assembly is actually formed in afirst injection molding process where the dielectric material used ispolyphenylene sulfide (PPS). Other similar materials are suitable andthe use of PPS is not critical. It is a dielectric (thus also anelectrical insulating material) which has the characteristic of bondingto itself. The mold for the injection molding process is not shown perse since it is obvious from the construction of FIG. 2. As alluded toabove, the back metal cylinder 24 has a smaller diameter inner cavity inthe section 27 as opposed to the larger inner cavity 23 which issuitable for mating with the outer conductor 14 (see FIG. 3). These twosections are connected by a stepped transition section 29 which willserve the purpose of physically limiting the insertion of the coaxialcable as will be discussed below.

The bridging section 26 is also formed so that the smaller diameterinner cavity 27 eventually mates with the smaller cavity 21 of the frontcylinder 22 by a series of truncated cones 31 and 32 (with the cone 32being a portion of the front cylinder 22).

In summary, so far, FIG. 2 illustrates a step of the invention where thefront and back pair of metal cylinders are formed and then in a firstinjection molding step they are molded together in spaced coaxialproximity. Next the coaxial cable 12 is trimmed as illustrated in FIG. 3so that the jacket 16 is cut away to expose outer conductor 14, aportion of the outer conductor is trimmed to expose the innercylindrical insulator 17a and a portion of this insulator is itselftrimmed to expose the end segment 13 of the center conductor. Thistrimmed cable end is then inserted into the front and back cylinderassembly of FIG. 2 as illustrated by the exploded view of FIG. 3.

However, to provide proper sealing, spacing and for the purpose ofmoisture proofing, the prepared coaxial cable 12 is first inserted intothe solder ring 33, a collar unit 34 which has a stepped end 36, and anelastomeric sleeve 37 which may be of an insulating material such asfluorosilicone rubber. Sleeve 37 has an outer diameter which matches theinner diameter of the smaller diameter cavity 27 of the back cylinder24. Sleeve 37 fits snugly over the exposed insulator 17a.

The completed assembly of FIG. 3 is shown in both FIGS. 1 and 5 when theentire exploded FIG. 3 is inserted in the front and back metal cylinderassembly 22, 24. As is best shown in FIG. 1, however, when the cable 12is inserted either manually or by machine, a one pound axial forceexerted as shown by the forces F1 and F2, deforms the elastomeric sleeve37 to completely fill the space in the end portion 27 of the backcylinder 24 and to cause the sleeve to deform against the conicaltransition 31 of the dielectric bridge 26. And at the other end sleeve37 abuts against the collar 34.

The above insertion is precisely limited by the mating of the steppedcollar end 36 with the step 29 of back cylinder which matches. Thisprovides for a manufacturing repeatability in the electromagneticcharacteristics of the entire proximity sensor which in the finalassembly must be calibrated.

After the above insertion, a permanent mechanical and electricalconnection is made between outer conductor 14 and the inner cavity 23 ofback cylinder 24. By the use of inductive heating with the above forceF1, F2 being applied, the heating temperature of approximately 450° F.melts the solder ring 33 causing it to flow over the exposed conductor14 affixing it permanently throughout its length to inner cavity 23. Andat the same time the solder provides for a permanent connection of thecollar 34 to back cylinder 24. Of course rather than solder, an adhesiveor even welding could be used.

Then in a second sequential step the front cylinder 22 and its innercavity 21 is electrically and mechanically connected to conductor 13 byfirst placing a measured amount of solder paste, indicated at 38, intothe end cavity 41 which flows into inner cavity 21 when heated. Theconductor 13 is then inserted and by a similar inductive heatingtechnique a permanent connection is made. Thus the assembly indicated at40 in FIG. 5 results. As discussed above a suitable adhesive or weldingcan be used instead of soldering. The measured amount of solder paste 38helps to provide effective repeatability of the electromagneticcharacteristics of the entire proximity sensor especially with respectto the inductance parameter of the coil 11 (illustrated in FIG. 1) whichis relatively close to center conductor 13. This repeat-ability will bediscussed in detail below.

As is also apparent from a close examination of FIG. 1, the front endportion of the inner cylindrical insulator 17a abuts the end of cylinder22.

FIG. 5 illustrates a second injection molding step with the samebondable dielectric material where a cylindrical jacket 45 is moldedover the front and back cylinders 22 and 24, and also bonds to thebridging material 26. The result of the molding is illustrated by theunit 42 in FIG. 6. As also shown in FIG. 6, the injection moldingmaterial extends over the outer insulating jacket 16 to prevent moisture(which causes electrical conduction) from penetrating. Referring back toFIG. 5, in the molding step an annular bobbin recess 43 is providedwhich is coaxial with the front and back cylinders 22 and 24 along witha pair of parallel tunnels 46 and 47 which terminate as best shown byunit 42 in FIG. 6, at the front cylinder 22 and the back cylinder 24,respectively. Moreover in the molding process appropriate spacesindicated at 48 and 49 are left open so that the leads 51 and 52 of coil11 may be inserted into the tunnels 46 and 47, respectively, andelectrical connection made to front cylinder 22 and back cylinder 24,such connection is illustrated in FIG. 1 at the spaces 48 and 49.

Specifically such electrical connection can be accomplished byresistance welding in a suitable jig where opposed welding electrodesare used at suitable apertures (not shown) left in the dielectricmaterial. And this can be done since the tunnels 46 and 47 are locatedat a relative 90° to each other.

Referring to FIG. 6, after the coil 11 is formed as a bobbin andinserted into the annular recess 43, the center post 53 of the recessaccurately coaxially centers the coil in the recess and locates itaxially with respect to the metal portions of the assembly such as thefront and back cylinders 22 and 24, and the various conductors. Thus asshown in FIG. 1 by the dimension L between coil 11 and the step 29, theelectromagnetic relationship of the coil is repeatedly and preciselyfixed with the remaining metal portions of the proximity sensor. Thisconstant dimension between the coil and metal portions thus allows cable12 to have a predetermined length with perhaps a plus or minus 10%tolerance which is independent of variations in manufactured proximitysensor units. With the final assembly of the entire sensing systemincluding the electronic portion (not shown) the coil 11 forms a portionof an electrical bridge where its variation in inductance and resistanceis the critical parameter in sensing eccentric movement of the motorshaft. A final calibration involves balancing the bridge in a mannerwell known in the art.

FIG. 7 illustrates a third injection molding step where the unit 42 withthe bobbin 11 installed at least has its forward portion encapsulated.This includes the bobbin 11 and its recess 43 and referring to FIG. 6the spaces 48 and 49. Also the tunnels 46 and 47 are filled to preventmoisture entering the assembly. The encapsulation is shown as 54 in FIG.7 and the final unit of course is illustrated at 56 in FIG. 8 with theshell encapsulation 54. It extends over the end of the coil 11 and overand into a groove 57 in the back cylinder 24. FIG. 7 illustrates theinjection molding gates 58a, 58b at the front and 59a and 59b at therear for forming the encapsulation unit 54. The mold (which of course isthe reverse of what is shown in FIG. 7) includes a narrowed ramp portionindicated at 61 which provides for a greater restriction of the materialflowing through gates 58a and 58b so that the bobbin recess is firstfilled and the coil 11 firmly fixed in the recess and then the tunnels46 and 47 are filled with the PPS material. This sequence prevents thefilling of the tunnels first from forcing the bobbin or coil 11 out ofits recess during the encapsulation molding process. In addition sincethe leads 51 and 52 (see FIG. 6) are lying along the tunnels 46 and 47so that the flow of the molding material is laminar (thus producing onlylaminar friction) this minimizes or prevent breakage of these leads.Such leads are very fragile being typically 0.035 inches in diameter. Atthe same time the filling of the tunnels fills in the spaces 48 and 49where the leads have been welded to respectively the front and backcylinders.

In the last injection molding step of the invention or the fourth, themetal case 10 is placed on the assembly 56 indicated in FIG. 8 alongwith the O-ring 60 which is inserted in the notch 62. Through gate 63shown in FIG. 1, PPS material is injected to affix the case to theoverall assembly. Since the coil 11 and its leads 51 and 52 have alreadybeen securely placed and protected by the previous injection moldingstep, there is no danger of damage to these portions with theinstallation of the case. Because of the use of the bondable PPSmaterial, the metal case 10 is effectively affixed to the previouslyinjection molded assembly so that it is mechanically stable and it issealed to resist moisture leaks which might otherwise affect theelectrical characteristics of the coil 11.

As discussed above, in addition to use as a proximity sensor, thepresent invention may be employed very broadly in the sensing field as,for example, a temperature sensor or a velocity pickup device. Forexample, when used as a temperature sensor the coil 11 would be a singlewire thermocouple of the RTD type which would be molded in the bobbinrecess. The protection from moisture and the sealing provided by theforegoing injection molding process and associated seals are stillefficacious, and the fragile leads coming from the thermocouple arehandled in the same manner. The only change in the process would be theuse of perhaps a thinner overall plastic casing in order to provide fora suitable heat transfer to the RTD temperature sensing coil.

Another use is as a velocity pickup where a "geophone" type housingcontaining a coil and magnet would also be placed in the bobbin recesswith associated leads being affixed to the shielded cable and metalcylinder.

From a broad standpoint, the inventive concept relates to any type ofshielded cable and associated coil in a case. The cable may only have asingle interior conductor which would extend into the inner cavity 21 ofa single cylinder. And then the injection molding would provide in afirst step both a recess for the sensing coil and a plastic connectionto the metal cylinder. And then in another injection molding step thecoil would be encapsulated to protect it from both physical harm andfrom moisture.

Thus in summary the present invention with its four step injectionmolding process and associated seals such as the elastomeric seal 37 andthe collar 34 provides a very efficient manufacturing alternative to theuse of many separate parts. At the same time, the manufacturing processallows for rigorous and/or precise control of dimensions so that theelectrical and mechanical characteristics of each manufactured sensorare repeatable. As discussed above the injection molding process allowsthe necessary mechanical and electrical connections to be made to ametal cylinder or other similar device to provide for durability of theunit as far as resisting axial and torsional forces. And then theinjection molding provides for the coupling to either one or bothcylinders, whatever is the case, and at the same time makes a convenientand accurately positioned recess for the sensing coil. Finally thesensing coil which is by its nature whether it is used for proximity,temperature or velocity, is very fragile and the injection moldingallows for protection and encapsulation of the coil and also protectionof the relatively fine leads. Lastly, especially in conjunction with theinvention's use as a proximity sensor, very close control of tolerancesare provided (as illustrated by the dimension L in FIG. 1) so that theelectrical characteristics and specifically the inductance of the coilcan be predetermined so that the related electrical instrumentation, forexample, to detect vibration parameters is easily calibrated.

FIGS. 9 through 21 illustrate another embodiment of the invention whichincludes a front cylinder 71 and back cylinder 72, both of conductivemetal, which have been molded together in spaced coaxial proximity bythe dielectric connector 73. As is true in the case of the previousembodiment, the inner diameters of the cylinders 71 and 72 will matchthe center conductor 74 (see FIG. 11) of the coaxial cable 70 and theouter conductor 76. In addition the cable is trimmed in the same manneras above. However, in the injection molding step, an annular recess isalso formed at 77 by the dielectric material 73 which includes a centerpost 78 on which as illustrated in FIGS. 9 and 10 also, a coil 79 isplaced. The dielectric material 73 contains suitable apertures as shownat 81 and 82 which allow the leads 83 and 84 to be respectivelyresistance welded to the cylinders 71 and 72 as shown in FIG. 10.

Referring to FIG. 11 the prepared coaxial cable 70, which of course hasbeen prepared as in the previous embodiment, has placed on it a solderpreformed ring 86 and a plastic protector sleeve 87 as illustrated inthe assembled drawing of FIG. 12. Sleeve 87 acts as a moisture seal forthe coaxial cable.

Next in FIG. 12 a plastic type conically shaped sleeve 88 is formed witha series of peripheral lugs 89 and as illustrated in FIG. 13 placed oncable 70 for later use. In addition, as illustrated in FIG. 13, asilicon lubricant is applied to moisture seal 87.

Referring to FIG. 14 the assembly previously assembled in FIG. 10 hassolder paste, indicated at 91, applied to the inside of the frontcylinder 71. Then as illustrated in FIGS. 15 and 16 the preparedassembly of molded together front and back cylinders 71, 72 with thecoil 79 in recess 77 is mated with the assembly of FIG. 13. One slidesinto the other as illustrated in FIG. 16 with inner conductor 74 incylinder 71 and outer conductor 76 in cylinder 72; the completed unit ispositioned in an inductive heating unit. FIG. 17 illustrates the resultsof such heating where the solder ring 86 (referred to in FIG. 16) hasnow permeated into the braided material 76 of the cable 70 toeffectively electrically and mechanically affix the braid to the rearcylinder 72; and in addition, as illustrated, for the center conductor74, the solder paste 91 previously applied has completely filled thecavity of the front cylinder 71 to again electrically and mechanicallyaffix this center conductor to the front cylinder. At the same timeelectrical contact has, of course, been made with the two leads 83 and84 and the coil 79.

The protective sleeve 88 as illustrated in FIG. 17, which was initiallyinstalled in the step of FIG. 15 before the cable 70 was attached to thedielectric assembly, is now slid into the position shown in FIG. 18 andsecured there both by an adhesive which is applied and by the wedgingaction of its conical shape against the conical envelope 93 of thedielectric material 73 which was formed in the initial step of theinvention shown in FIG. 9. As is clear from examination of FIG. 18, theprotective sleeve covers the relatively fragile conductors or leads 83and 84 of the coil 89. In addition, the periphery of the coil 89 is alsoprotected and centered by the sleeve.

The next step as shown in FIG. 19 is an encapsulation step where theentire assembly of FIG. 18 is placed in an encapsulation mold. Here thefinal encapsulation is illustrated by the cylindrical jacket 94 which,of course, is the result of the negative mold (not shown) which hassurrounded it. The molding process thus completes the attachment of thesleeve 88 to the remainder of the assembly. Also the mold material isthe same bondable dielectric material which is used in the originalmaterial 73.

In the molding process the lugs 89 of the sleeve 88 provide for accuratethickness control of the face 96 of the cylindrical jacket which forms acover over the front of the coil 89. Thus by the use of the lugs 89 thethickness of the cover 96 can be accurately controlled. This isimportant in a proximity sensor since the spacing from the rotatingshaft is critical. In addition the sleeve 88 during the molding processinsures that the coil 89 is still centered and concentric within theentire encapsulation 94. Thus the lugs 89 again provide limits in theholding process. Another advantage of the sleeve 88 is that it serves asa protector of coils and leads from the high pressure molding fluid.

Finally as illustrated in FIGS. 19 and 20, a threaded metal case 97 isslid onto the cable 70 and meshed by crimping 98 to the envelope 94. Andalso as illustrated in FIG. 20 a connector unit 99 is placed on cable70.

FIG. 21 illustrates a variation of the molding step of FIG. 19 wherebefore such molding a preformed plastic cap 101 is placed over coil 89and that end of the assembly; the metal case 97 is also slid into place.Then through appropriate gates 102, the molding and encapsulation takesplace, where a cylindrical jacket 103 is formed to lock into place bothcase 97 and cap 101. Thus, this second molding step serves two purposes.

Thus an improved process for forming a proximity sensor has beenprovided.

What is claimed is:
 1. A process for making a proximity sensor having ametal case with a sensing coil at one end and a coaxial cable extendingout of the other end for connecting to an electrical processing unit,the coaxial cable having an outer insulating jacket and a wire braidouter conductor surrounding an inner cylindrical insulator carrying acenter conductor, the process comprising the following steps:trimming anend of said coaxial cable so that said jacket is cut away to expose saidouter conductor, which has a predetermined outer diameter, and trimminga portion of said outer conductor and inner cylindrical insulator toexpose an end segment of said center conductor, which has apredetermined diameter; forming a front and back pair of metal cylinderswith said front cylinder having an inner cavity with a diametersubstantially matching the diameter of said center conductor and saidback cylinder having an inner cavity with a diameter substantiallymatching the diameter of said outer conductor; in a first injectionmolding step molding together in spaced coaxial proximity with abridging dielectric material which bonds to itself, said front and backmetal cylinders; inserting said trimmed cable end into said innercavities of said molded together front and back cylinders andmechanically and electrically connecting said outer conductor to saidback cylinder and said center conductor to said front cylinder to resistaxial forces; in a second injection molding step with said bondabledielectric material, molding a cylindrical jacket over said front andback cylinders and bonding to said bridging material, said secondmolding providing an annular bobbin recess near said front cylinder andcoaxial therewith and also providing a pair of parallel tunnels leadingfrom said recess with one tunnel terminating at said front cylinder andthe other terminating at said back cylinder; forming said coil into theshape of a bobbin with two leads and inserting said coil in said bobbinrecess while inserting said leads through said tunnels, and electricallyattaching said leads to said front and back cylinders respectively; in athird injection molding step encapsulating at least said coil; insertingthe assembly of the above steps into said metal case; and in a fourthinjection molding step affixing said case to said assembly with saidbondable dielectric material.
 2. A process as in claim 1 where in saidinserting step said back cylinder is first connected to said outerconductor with use of a solder ring, and application of heat and a axialforce and then said front cylinder is connected to said centerconductor.
 3. A process as in claim 2 where a measured amount of solderpaste is placed into said front cylinder cavity which is heated to makesaid connection of said center conductor.
 4. A process as in claim 2including the step of abutting a collar with a stepped end against saidend of said exposed outer conductor, said stepped end having an outerdiameter matching the outer diameter of said outer conductor, said backcylinder's inner cavity including a matching step serving as atransition to a smaller diameter inner cavity, said step mating withsaid stepped end to limit said insertion.
 5. A process as in claim 1where in said second injection molding step said cylindrical jacketextends to and over said outer insulating jacket.
 6. A process as inclaim 1 where in said third injection molding step said dielectricmaterial fills spaces where said leads are attached to said front andback cylinders and fills said tunnels to thereby electrically insulatesaid front and back metal cylinders.
 7. A process as in claim 6 where insaid third injection molding step said bobbin recess is firstencapsulated and then said tunnels are filled to prevent such filling oftunnels from forcing said bobbin out of said recess.
 8. A process as inclaim 7 where said filling of said tunnels exerts only laminar frictionagainst said leads in said tunnels to prevent breakage of said leads. 9.A process as in claim 7 where a higher resistance to said material flowto said tunnels compared to said recess is provided.
 10. A process as inclaim 9 where said higher resistance is provided by a narrowed path. 11.A process as in claim 1 where in said trimming step a portion of saidinner cylindrical insulator between said center and outer conductors isexposed and where in said inserting step an insulating elastomer sleeveis placed over said exposed portion of said inner insulator.
 12. Aprocess as in claim 4 where in said trimming step a portion of saidinner cylindrical insulator between said center and outer conductors isexposed and where in said inserting step an insulating elastomer sleeveis placed over said exposed portion of said inner insulator, said sleeveabutting against said collar, said sleeve having an outer diametermatching the inner diameter of the smaller diameter cavity of said backcylinder, the other end of said sleeve abutting against said bridgingdielectric to provide a moisture seal.
 13. A process as in claim 11where said inner cylindrical insulator is formed of two layers with therelative outer layer spacing said outer conductor from the relativeinner layer which provides said exposed portion of said inner insulator.14. A process for making a sensor with a sensing coil at one end and ashielded cable extending out of the other end for connecting to anelectrical processing unit, the cable having an outer insulating jacketand an outer shielding conductor surrounding an inner cylindricalinsulator carrying at least one center conductor, the process comprisingthe following steps:trimming an end of said cable so that said jacket iscut away to expose said outer conductor, which has a predetermined outerdiameter, and trimming a portion of said outer conductor and innercylindrical insulator to expose an end segment of said center conductor,which has a predetermined diameter; forming a front and back pair ofmetal cylinders with said front cylinder having an inner cavity with adiameter substantially matching the diameter of said center conductorand said back cylinder having an inner cavity with a diametersubstantially matching the diameter of said outer conductor; in a firstinjection molding step molding together in spaced coaxial proximity witha bridging dielectric material which bonds to itself, said front andback metal cylinders; inserting said trimmed cable end into said innercavities of said molded together front and back cylinders andmechanically and electrically connecting said outer conductor to saidback cylinder and said center conductor to said front cylinder to resistaxial forces; in a second injection molding step with said bondabledielectric material, molding a cylindrical jacket over said front andback cylinders and bonding to said bridging material, said secondmolding providing an annular bobbin recess near said front cylinder andcoaxial therewith and also providing a pair of tunnels leading from saidrecess with one tunnel terminating at said front cylinder and the otherterminating at said back cylinder; forming said coil into the shape of abobbin with two leads and inserting said bobbin in said bobbin recesswhile inserting said leads through said tunnels and electricallyattaching said leads to said front and back cylinders respectively. 15.A process for making a sensor with a sensing coil at one end having atleast one lead and a shielded cable extending out of the other end forconnecting to an electrical processing unit, the cable having an outerinsulating jacket and an outer shielding conductor surrounding an innerinsulator carrying at least one interior conductor, the processcomprising the following steps:trimming an end of said cable so thatsaid jacket and outer shielding conductor is cut away to expose an endsegment of said interior conductor; forming at least one metal cylinderhaving an inner cavity to accommodate said interior conductor; in oneinjection molding step with a bondable dielectric material, molding acylindrical jacket over said cylinder and providing a coil recess nearsaid cylinder and substantially coaxial therewith and also providing atleast one tunnel leading from said recess and terminating at saidcylinder; inserting said coil in said coil recess while inserting saidlead through said tunnel and electrically attaching said lead to saidcylinder; and in another injection molding step encapsulating at leastsaid coil with said dielectric material.
 16. A process for making asensor with a sensing coil at one end and a shielded cable extending outof the other end for connecting to an electrical processing unit, thecable having an outer insulating jacket and an outer shielding conductorsurrounding an inner cylindrical insulator carrying at least one centerconductor, the process comprising the following steps:trimming an end ofsaid cable so that said jacket is cut away to expose said outerconductor, which has a predetermined outer diameter, and trimming aportion of said outer conductor and inner cylindrical insulator toexpose an end segment of said center conductor, which has apredetermined diameter; forming a front and back pair of metal cylinderswith said front cylinder having an inner cavity with a diametersubstantially matching the diameter of said center conductor and saidback cylinder having an inner cavity with a diameter substantiallymatching the diameter of said outer conductor; in a first injectionmolding step molding together in spaced coaxial proximity with abridging dielectric material which bonds to itself, said front and backmetal cylinders and providing in such molding step an annular bobbinrecess near said front cylinder; forming said coil into the shape of abobbin with two leads and inserting said bobbin in said bobbin recessand welding said leads respectively to said front and back cylinders;inserting said trimmed cable end into said inner cavities of said moldedtogether front and back cylinders and mechanically and electricallyconnecting said outer conductor to said back cylinder and said centerconductor to said front cylinder to resist axial forces; fixing aprotective sleeve over said coil and leads; in a second injectionmolding step with said bondable dielectric material, molding acylindrical jacket over said front and back cylinders and bonding tosaid bridging material including providing a cover over the face of saidcoil and bobbin recess.
 17. A process for making a sensor as in claim 16where in said first molding step a conical envelope of material isformed over said front cylinder and where said protective sleeve isconically shaped to mate therewith.
 18. A process for making a sensor asin claim 16 including the step of inserting the assembly of the aboveinto a metal case.
 19. A process for making a sensor as in claim 16where said bobbin recess is formed by a central post on which said coilis placed whereby said sleeve protects the periphery of said coil andcenters it in said second molding step.
 20. A process as in claim 16where in said second injection molding step said cover over the faceincludes a preformed cap which is fixed by said molding and the aboveassembly is first inserted into a metal case whereby said cylindricaljacket is formed between said case and said assembly.
 21. A process asin claim 16 where said cover is formed as part of said cylindricaljacket.